Term
| What is a lysosome known as in plant cells? |
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Definition
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Term
| What is the role of a lysosome? |
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Definition
| degrades macromolecules & cellular organelles/components |
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Term
| How are resident lysosomal membrane proteins protected from degradation? |
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Definition
| carbohydrate groups are attached to the lumenal side of these proteins, protecting them from degradation |
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Term
| How is the low pH of the lysosome maintained? |
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Definition
| ATPase proton pump, pumps H+ into lumen from cytosol |
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Term
| How are lysosomal cargo proteins trafficked from the late endosome to the lysosome? |
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Definition
1. Cargo proteins are partitioned into a specific portion of the late endosome
2. MVB fragments off from endosome
3. MVB fuses with lysosome, membrane proteins move laterally into lysosomal mmb, contents are released into lysosome |
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Term
| What happens to lysosomal cargo proteins once they are released into the lysosome? What about the intralumenal vesicles? |
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Definition
acidic pH of lysosomal lumen activates hydrolase enzymes
intralumenal vesicles are degraded |
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Term
| What is the unique morphology of the MVB? |
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Definition
| contains intralumenal vesicles formed by invagination of the MVB membrane |
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Term
| What is the difference between endocytosis & phagocytosis? |
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Definition
endocytosis: selective internalization of components of the PM
phagocytosis: uptake of large materials from extracellular space |
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Term
| What are the 2 forms of endocytosis? |
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Definition
1. bulk-phase endocytosis (pinocytosis)
2. receptor-mediated endocytosis |
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Term
True or False
pinocytosis / bulk-phase endocytosis is highly selective |
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Definition
False
it is responsible for non-specific uptake of extracellular fluids |
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Term
| How are PM proteins destined for degradation & various PM receptors internalized in the cell? |
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Definition
| receptor-mediated endocytosis |
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Term
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Definition
| indentations in the PM where receptors accumulate & internalization takes place |
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Term
| What protein is found in the inner leaflet of coated pits, and what is its function? |
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Definition
PI(4,5)P2
-recruits adapter protein AP2 to the coated pits |
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Term
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Definition
| a linker protein with multiple binding sites, will recruit clathrin triskelions from the cytosol |
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Term
| What is the main driving force in membrane curvature? |
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Definition
| assembly of the clathrin triskelion lattice |
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Term
| After an endocytic vesicle has budded off, where does it go? |
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Definition
| targets to the early endosome |
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Term
| What mediates the transport of vesicles to/from endosomes? |
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Definition
| Rab & SNARE proteins & cytoskeletal elements |
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Term
| What is the function of the early endosome? |
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Definition
| responsible for sorting & recycling extracellular materials via endocytosis |
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Term
| What are the two compartments of the early endosome? |
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Definition
| recycling compartment & sorting compartment |
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Term
| What happens to the recycling compartment of the early endosome? |
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Definition
| detaches & traffics back to the PM |
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Term
| What happens to the sorting compartment of the early endosome? |
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Definition
| -matures into a late endosome, with an ATP-ase pump driving protons into the lumen to lower pH |
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Term
| What results from the lowering of the pH of the late endosome? |
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Definition
| incoming M6P receptor-lysosomal cargo proteins from TGN dissociate |
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Term
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Definition
Multivesicular Body
-late endosomal fragment |
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Term
| What is found within an MVB? |
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Definition
| endocytic cargo, intralumenal vesicles & soluble cargo proteins from the TGN |
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Term
| What is the purpose of inward vesiculation of the MVB membrane? |
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Definition
-receptors on outside of late endosome need to make their way inside to be degraded
-if they join lumen surrounded by late endosome proteins, the attached carbohydrate groups will protect them from degradation
-formation of intralumenal vesicles containing these receptors ensures they will be degraded |
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Term
| What happens when the MVB fuses with the lysosome? |
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Definition
-all materials are released into lumen of lysosome
-soluble cargo proteins are activated
-endocytic cargo & intralumenal vesicles are degraded |
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